Deoxyribonucleic Acid Homology Studies of Lactobacillus casei, Lactobacillus paracasei sp. nov., subsp. paracasei and subsp. tolerans, and Lactobacillus rhamnosus sp. nov., comb. nov.

Deoxyribonucleic acid (DNA)-DNA hybridizations were performed on strains of Lactobacillus casei. Our results indicate that this species as presently constituted is genomically very heterogeneous. The majority of strains designated L. casei subsp. casei, together with members of L. casei subsp. alactosus, L. casei subsp. pseudoplantarum, and L. casei subsp. tolerans, exhibited high levels of DNA relatedness with each other but were distinct from the type strain of L. casei subsp. casei. Strains of L. casei subsp. rhamnosus also formed a genomically homogeneous group unrelated to all members of the other L. casei subspecies examined. On the basis of the present and previous findings we suggest that members of L. casei subsp. alactosus, L. casei subsp. pseudoplantarum, and L. casei subsp. tolerans and the majority of L. casei subsp. casei strains be given separate species status, for which we propose the names L. paracasei sp. nov., L. paracasei subsp. paracasei (type strain, NCDO 151), and L. paracasei subsp. tolerans (type strain ATCC 25599). We also propose that L. casei subsp. rhamnosus be elevated to species status, as L. rhamnosus sp. nov. (type strain, ATCC 7469).